<!DOCTYPE html>
<html lang="en-US">
  <head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=Edge">
    <meta name="viewport" content="initial-scale=1.0, user-scalable=no, width=device-width">
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/font-awesome/4.4.0/css/font-awesome.min.css" type="text/css">
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css" type="text/css">
    <link rel="stylesheet" href="./resources/prism/prism.css" type="text/css">
    <link rel="stylesheet" href="../css/ol.css" type="text/css">
    <link rel="stylesheet" href="./resources/layout.css" type="text/css">
    
    
    <script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=fetch,requestAnimationFrame,Element.prototype.classList,URL"></script>
    <script src="./resources/zeroclipboard/ZeroClipboard.min.js"></script>
    <title>Layer Clipping with WebGL</title>
  </head>
  <body>

    <header class="navbar" role="navigation">
      <div class="container">
        <div class="display-table pull-left" id="navbar-logo-container">
          <a class="navbar-brand" href="./"><img src="./resources/logo-70x70.png">&nbsp;OpenLayers Examples</a>
        </div>
        <!-- menu items that get hidden below 768px width -->
        <nav class='collapse navbar-collapse navbar-responsive-collapse'>
          <ul class="nav navbar-nav pull-right">
            <li><a href="../doc">Docs</a></li>
            <li><a class="active" href="index.html">Examples</a></li>
            <li><a href="../apidoc">API</a></li>
            <li><a href="https://github.com/openlayers/ol3">Code</a></li>
          </ul>
        </nav>
      </div>
    </header>

    <div class="container-fluid">

      <div id="latest-check" class="alert alert-warning alert-dismissible" role="alert" style="display:none">
        <button id="latest-dismiss" type="button" class="close" data-dismiss="alert" aria-label="Close"><span aria-hidden="true">&times;</span></button>
        This example uses OpenLayers v<span>3.20.0</span>. The <a id="latest-link" href="#" class="alert-link">latest</a> is v<span id="latest-version"></span>.
      </div>

      <div class="row-fluid">
        <div class="span12">
          <h4 id="title">Layer Clipping with WebGL</h4>
          <div id="map" class="map"></div>
<div id="no-webgl" class="alert alert-danger" style="display: none">
  This example requires a browser that supports <a href="http://get.webgl.org/">WebGL</a>.
</div>

        </div>
      </div>

      <div class="row-fluid">
        <div class="span12">
          <p id="shortdesc">Layer WebGL clipping example.</p>
          <div id="docs"><p>This example shows how to use the <code>precompose</code> and <code>postcompose</code> rendering hooks to clip layers using WebGL.</p>
</div>
          <div id="api-links">Related API documentation: <ul class="inline"><li><a href="../apidoc/ol.Map.html" title="API documentation for ol.Map">ol.Map</a></li>,<li><a href="../apidoc/ol.View.html" title="API documentation for ol.View">ol.View</a></li>,<li><a href="../apidoc/ol.control.html" title="API documentation for ol.control">ol.control</a></li>,<li><a href="../apidoc/ol.has.html" title="API documentation for ol.has">ol.has</a></li>,<li><a href="../apidoc/ol.layer.Tile.html" title="API documentation for ol.layer.Tile">ol.layer.Tile</a></li>,<li><a href="../apidoc/ol.source.OSM.html" title="API documentation for ol.source.OSM">ol.source.OSM</a></li></ul></div>
        </div>
      </div>

      <div class="row-fluid">
        <div id="source-controls">
          <a id="copy-button"><i class="fa fa-clipboard"></i> Copy</a>
          <a id="jsfiddle-button"><i class="fa fa-jsfiddle"></i> Edit</a>
        </div>
        <form method="POST" id="jsfiddle-form" target="_blank" action="https://jsfiddle.net/api/post/library/pure/">
          <textarea class="hidden" name="js">if (!ol.has.WEBGL) {
  var info &#x3D; document.getElementById(&#x27;no-webgl&#x27;);
  /**
   * display error message
   */
  info.style.display &#x3D; &#x27;&#x27;;
} else {

  var osm &#x3D; new ol.layer.Tile({
    source: new ol.source.OSM()
  });

  var map &#x3D; new ol.Map({
    layers: [osm],
    renderer: /** @type {ol.renderer.Type} */ (&#x27;webgl&#x27;),
    target: &#x27;map&#x27;,
    controls: ol.control.defaults({
      attributionOptions: /** @type {olx.control.AttributionOptions} */ ({
        collapsible: false
      })
    }),
    view: new ol.View({
      center: [0, 0],
      zoom: 2
    })
  });

  var fragmentShaderSource &#x3D; [
    &#x27;precision mediump float;&#x27;,
    &#x27;void main() {&#x27;,
    &#x27;}&#x27;
  ].join(&#x27;&#x27;);

  var vertexShaderSource &#x3D; [
    &#x27;attribute vec2 a_position;&#x27;,
    &#x27;void main() {&#x27;,
    &#x27;  gl_Position &#x3D; vec4(a_position, 0, 1);&#x27;,
    &#x27;}&#x27;
  ].join(&#x27;&#x27;);

  osm.on(&#x27;precompose&#x27;, function(event) {
    var context &#x3D; event.glContext;

    var gl &#x3D; context.getGL();
    var program &#x3D; gl.createProgram();

    var vertexShader &#x3D; gl.createShader(gl.VERTEX_SHADER);
    gl.shaderSource(vertexShader, vertexShaderSource);
    gl.compileShader(vertexShader);
    gl.attachShader(program, vertexShader);

    var fragmentShader &#x3D; gl.createShader(gl.FRAGMENT_SHADER);
    gl.shaderSource(fragmentShader, fragmentShaderSource);
    gl.compileShader(fragmentShader);
    gl.attachShader(program, fragmentShader);

    gl.linkProgram(program);
    context.useProgram(program);

    var positionLocation &#x3D; gl.getAttribLocation(program, &#x27;a_position&#x27;);

    gl.enable(gl.STENCIL_TEST);
    gl.colorMask(false, false, false, false);
    gl.stencilOp(gl.KEEP, gl.KEEP, gl.REPLACE);
    gl.stencilFunc(gl.ALWAYS, 1, 0xff);

    var buffer &#x3D; gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
      // first band
      -1.0, -1.0, -0.75, -1.0, -1.0, 1.0,
      -1.0, 1.0, -0.75, -1.0, -0.75, 1.0,
      // second band
      -0.5, -1.0, -0.25, -1.0, -0.5, 1.0,
      -0.5, 1.0, -0.25, -1.0, -0.25, 1.0,
      // third band
      0.0, -1.0, 0.25, -1.0, 0.0, 1.0,
      0.0, 1.0, 0.25, -1.0, 0.25, 1.0,
      // forth band
      0.5, -1.0, 0.75, -1.0, 0.5, 1.0,
      0.5, 1.0, 0.75, -1.0, 0.75, 1.0
    ]), gl.STATIC_DRAW);

    gl.enableVertexAttribArray(positionLocation);
    gl.vertexAttribPointer(positionLocation, 2, gl.FLOAT, false, 0, 0);
    gl.drawArrays(gl.TRIANGLES, 0, 24);

    gl.bindBuffer(gl.ARRAY_BUFFER, null);
    gl.deleteBuffer(buffer);

    gl.colorMask(true, true, true, true);
    gl.stencilFunc(gl.NOTEQUAL, 0, 0xff);
    gl.stencilOp(gl.KEEP, gl.KEEP, gl.KEEP);
  });

  osm.on(&#x27;postcompose&#x27;, function(event) {
    var context &#x3D; event.glContext;
    var gl &#x3D; context.getGL();
    gl.disable(gl.STENCIL_TEST);
  });
}
</textarea>
          <textarea class="hidden" name="css"></textarea>
          <textarea class="hidden" name="html">&lt;div id&#x3D;&quot;map&quot; class&#x3D;&quot;map&quot;&gt;&lt;/div&gt;
&lt;div id&#x3D;&quot;no-webgl&quot; class&#x3D;&quot;alert alert-danger&quot; style&#x3D;&quot;display: none&quot;&gt;
  This example requires a browser that supports &lt;a href&#x3D;&quot;http://get.webgl.org/&quot;&gt;WebGL&lt;/a&gt;.
&lt;/div&gt;
</textarea>
          <input type="hidden" name="wrap" value="l">
          <input type="hidden" name="resources" value="https://openlayers.org/en/v3.20.0/css/ol.css,https://openlayers.org/en/v3.20.0/build/ol.js">
        </form>
        <pre><code id="example-source" class="language-markup">&lt;!DOCTYPE html&gt;
&lt;html&gt;
  &lt;head&gt;
    &lt;title&gt;Layer Clipping with WebGL&lt;/title&gt;
    &lt;link rel="stylesheet" href="https://openlayers.org/en/v3.20.0/css/ol.css" type="text/css"&gt;
    &lt;!-- The line below is only needed for old environments like Internet Explorer and Android 4.x --&gt;
    &lt;script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"&gt;&lt;/script&gt;
    &lt;script src="https://openlayers.org/en/v3.20.0/build/ol.js"&gt;&lt;/script&gt;
  &lt;/head&gt;
  &lt;body&gt;
    &lt;div id&#x3D;&quot;map&quot; class&#x3D;&quot;map&quot;&gt;&lt;/div&gt;
    &lt;div id&#x3D;&quot;no-webgl&quot; class&#x3D;&quot;alert alert-danger&quot; style&#x3D;&quot;display: none&quot;&gt;
      This example requires a browser that supports &lt;a href&#x3D;&quot;http://get.webgl.org/&quot;&gt;WebGL&lt;/a&gt;.
    &lt;/div&gt;
    &lt;script&gt;
      if (!ol.has.WEBGL) {
        var info &#x3D; document.getElementById(&#x27;no-webgl&#x27;);
        /**
         * display error message
         */
        info.style.display &#x3D; &#x27;&#x27;;
      } else {

        var osm &#x3D; new ol.layer.Tile({
          source: new ol.source.OSM()
        });

        var map &#x3D; new ol.Map({
          layers: [osm],
          renderer: /** @type {ol.renderer.Type} */ (&#x27;webgl&#x27;),
          target: &#x27;map&#x27;,
          controls: ol.control.defaults({
            attributionOptions: /** @type {olx.control.AttributionOptions} */ ({
              collapsible: false
            })
          }),
          view: new ol.View({
            center: [0, 0],
            zoom: 2
          })
        });

        var fragmentShaderSource &#x3D; [
          &#x27;precision mediump float;&#x27;,
          &#x27;void main() {&#x27;,
          &#x27;}&#x27;
        ].join(&#x27;&#x27;);

        var vertexShaderSource &#x3D; [
          &#x27;attribute vec2 a_position;&#x27;,
          &#x27;void main() {&#x27;,
          &#x27;  gl_Position &#x3D; vec4(a_position, 0, 1);&#x27;,
          &#x27;}&#x27;
        ].join(&#x27;&#x27;);

        osm.on(&#x27;precompose&#x27;, function(event) {
          var context &#x3D; event.glContext;

          var gl &#x3D; context.getGL();
          var program &#x3D; gl.createProgram();

          var vertexShader &#x3D; gl.createShader(gl.VERTEX_SHADER);
          gl.shaderSource(vertexShader, vertexShaderSource);
          gl.compileShader(vertexShader);
          gl.attachShader(program, vertexShader);

          var fragmentShader &#x3D; gl.createShader(gl.FRAGMENT_SHADER);
          gl.shaderSource(fragmentShader, fragmentShaderSource);
          gl.compileShader(fragmentShader);
          gl.attachShader(program, fragmentShader);

          gl.linkProgram(program);
          context.useProgram(program);

          var positionLocation &#x3D; gl.getAttribLocation(program, &#x27;a_position&#x27;);

          gl.enable(gl.STENCIL_TEST);
          gl.colorMask(false, false, false, false);
          gl.stencilOp(gl.KEEP, gl.KEEP, gl.REPLACE);
          gl.stencilFunc(gl.ALWAYS, 1, 0xff);

          var buffer &#x3D; gl.createBuffer();
          gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
          gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
            // first band
            -1.0, -1.0, -0.75, -1.0, -1.0, 1.0,
            -1.0, 1.0, -0.75, -1.0, -0.75, 1.0,
            // second band
            -0.5, -1.0, -0.25, -1.0, -0.5, 1.0,
            -0.5, 1.0, -0.25, -1.0, -0.25, 1.0,
            // third band
            0.0, -1.0, 0.25, -1.0, 0.0, 1.0,
            0.0, 1.0, 0.25, -1.0, 0.25, 1.0,
            // forth band
            0.5, -1.0, 0.75, -1.0, 0.5, 1.0,
            0.5, 1.0, 0.75, -1.0, 0.75, 1.0
          ]), gl.STATIC_DRAW);

          gl.enableVertexAttribArray(positionLocation);
          gl.vertexAttribPointer(positionLocation, 2, gl.FLOAT, false, 0, 0);
          gl.drawArrays(gl.TRIANGLES, 0, 24);

          gl.bindBuffer(gl.ARRAY_BUFFER, null);
          gl.deleteBuffer(buffer);

          gl.colorMask(true, true, true, true);
          gl.stencilFunc(gl.NOTEQUAL, 0, 0xff);
          gl.stencilOp(gl.KEEP, gl.KEEP, gl.KEEP);
        });

        osm.on(&#x27;postcompose&#x27;, function(event) {
          var context &#x3D; event.glContext;
          var gl &#x3D; context.getGL();
          gl.disable(gl.STENCIL_TEST);
        });
      }
    &lt;/script&gt;
  &lt;/body&gt;
&lt;/html&gt;</code></pre>
      </div>
    </div>

    <script src="./resources/common.js"></script>
    <script src="./resources/prism/prism.min.js"></script>
    <script src="loader.js?id=layer-clipping-webgl"></script>
  </body>
  <script>
  var packageUrl = 'https://raw.githubusercontent.com/openlayers/openlayers.github.io/build/package.json';
  fetch(packageUrl).then(function(response) {
    return response.json();
  }).then(function(json) {
    var latestVersion = json.version;
    document.getElementById('latest-version').innerHTML = latestVersion;
    var url = window.location.href;
    var branchSearch = url.match(/\/([^\/]*)\/examples\//);
    var cookieText = 'dismissed=-' + latestVersion + '-';
    var dismissed = document.cookie.indexOf(cookieText) != -1;
    if (!dismissed && /^v[0-9\.]*$/.test(branchSearch[1]) && '3.20.0' != latestVersion) {
      var link = url.replace(branchSearch[0], '/latest/examples/');
      fetch(link, {method: 'head'}).then(function(response) {
        var a = document.getElementById('latest-link');
        a.href = response.status == 200 ? link : '../../latest/examples/';
      });
      var latestCheck = document.getElementById('latest-check');
      latestCheck.style.display = '';
      document.getElementById('latest-dismiss').onclick = function() {
        latestCheck.style.display = 'none';
        document.cookie = cookieText;
      }
    }
  });
  </script>
</html>
